1) Field of the Invention
This invention relates generally to the fabrication of contact openings in semiconductor devices and more particularly to a method for forming a contact opening that has a reduced aspect ratio in an insulating layer that exposes a substrate.
2) Description of the Prior Art
High density integrated circuit technology requires the use of an insulating layer separating layers of metal electrode patterns formed over a semiconductor substrate containing device elements. Contact holes must be formed in the insulating layer to formed electrical connection to the contact areas in the semiconductor substrate. These contact opening require good metal step coverage to insure reliable electrical contact with low contact resistance. For high density circuits, good metal step coverage requires a contact via hole openings with lower effective aspect ratios.
FIG. 11 shows a conventional (prior art) contact hole 17 through an insulating layer to expose a contact area in the substrate. Generally in semiconductor products, the aspect ratio is less than or equal to 3 (depth to width ratio). However, for the inventor's recent DRAM and embedded DRAM products, due to high heights in the cell area, very high aspect ratios up to 7 are now being formed. However, the conventional straight contact hole causes problems and can not be used when aspect ratios much above 3 are used. When sputtered Ti or TiN barrier layers are formed over the contact hole, the Ti or TiN layer has a high resistance and a poor profile at the sidewalls and bottom.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering U.S. Pat. No. 5,629,237 (Wang) that shows a method of forming a tapered contact hole using a dry etch process.
U.S. Pat. No. 5,371,042 (Ong) shows a method for forming a contact hole having faceted top corners.
U.S. Pat. No. 5,686,354 (Avanzino et al.) shows a dual damascene process to from a via using a spacer.
There is still a need to form contact holes which allow better metal coverage with minimizing the contact area to the substrate.